

#box{
    width: 700px;
    height: 500px;
    border:2px solid #ccc;
    margin-left: 50%;
    margin-top: 50px;
    border-radius: 20px;
}
#box>h3{
    text-align: center;
    line-height: 50px;
    font-size: 20px;
}
#box #username,#sex,#age,#phone,#class,button,#address{
    width: 100%;
    margin-left: 20px;
    font-size: 18px;
    margin-top: 13px;
    font-family: "Bitstream Vera Sans Mono", Monaco, "Courier New", Courier, monospace;
}
#username>input,#age>input{
    width: 500px;
    display: inline;
}
#phone>input,#class>input,#address>input{
     width: 463px;
    display: inline;
}
button{
    width: 500px;
    margin-top: 15px;
    margin-left: 75px;
}

#username_error,#age_error,#phone_error,#address_error,#class_error{
    height: 15px;
    color: red;
    font-size: 15px;
}

.alert{
    width: 850px;
    height: 40px;
    text-align: center;
    position: relative;
    left: 25%;
    top: 20px;
    display: none;
}

.active{
    display: block;
}

#alert{
    width: 400px;
    margin:20px auto;
    text-align: center;
    display: none;
}